As opposed to invasive blood pressure measurement, non-invasive blood pressure measurement is a method of measuring the blood pressure of a human body indirectly. Currently, there are two categories of non-invasive blood pressure measurement methods.
One method is the auscultation measurement method on the basis of auscultation, i.e. the Korotkoff sound method. In the Korotkoff sound method, the cuff needs to be wound around the arm of the person whose blood pressure is to be measured and the stethoscope is placed at the brachial artery. Firstly, the cuff is inflated until the flow of the blood in the artery is blocked and then the cuff is deflated. A sound change will be generated during the inflation process, and the sound is referred to as Korotkoff sound. Doctors determine the blood pressure by listening to the change of the Korotkoff sound; this is referred to as the Korotkoff sound method.
The other method is the oscillometric method. Actually, the oscillometric method is an extension of the Korotkoff sound method. It blocks the flow of blood by inflating the cuff and then the cuff is deflated slowly. The blood pressure is determined by detecting the oscillation wave caused by the pulsation of the artery during the deflation process.
Currently, most of the electronic automatic blood pressure measuring devices measure the blood pressure based on the oscillometric method which has a high repeatability, consistency and accuracy and has been widely used in clinical examination.
U.S. Pat. No. 7,594,892 discloses a device for non-invasive blood pressure measurement and a safety protection method. The safety protection circuit of the measuring device is independently arranged with an auxiliary pressure measurement circuit and an auxiliary micro-processor circuit. In a normal measurement, the auxiliary micro-processor circuit periodically samples the pressure of a cuff by means of the auxiliary pressure measurement circuit and compares the sampled pressure with a nominal over-voltage protection value. If it exceeds the nominal over-voltage protection value, the auxiliary micro-processor circuit sends out a control signal to open a deflation valve until the air pressure falls below a safety pressure.
In view of the wide application of the non-invasive blood measurement, inventors of the present invention realize that the non-invasive pressure measurement has to meet certain particular requirements for particular people such as newborn babies. A newborn baby uses a relatively smaller cuff because it has relatively thinner arms. During the non-invasive blood measurement, if the cuff inflation speed is not controlled or not well controlled, there may be an over-voltage phenomenon caused by a very high inflation speed, which may make the newborn baby feel uncomfortable and thus impact the blood pressure measurement.
Furthermore, if a low cuff inflation speed is applied to avoid the over-voltage phenomenon, the measurement time may be very long due to the very low inflation speed. If the newborn baby cries because it has to lie in one position for a very long time, this may impact the accuracy of the measurement result.
Therefore, during the non-invasive blood pressure measurement of a newborn baby, it is very important to know how to control the cuff inflation. The solution disclosed by U.S. Pat. No. 7,594,892 can only solve the over-voltage problem by deflation if the pressure of the cuff exceeds the nominal over-voltage protection value. It cannot reduce or eliminate the over-voltage phenomenon during the process of inflating the cuff and it cannot solve the problem of the low cuff inflation speed.